No, they're not electrically powered, but given that you can buy an electrically-powered 5-horn kit from eBay for $20, it's certainly the cheapest way to go for a typical HN-reading hobbyist/hacker. Getting 14 horns is then $60, and the rest is relays a microcontroller, and a bit of 3D printing for the horns.

Which is an interesting nerd-sniping exercise in itself: https://www.grc.com/acoustics/an-introduction-to-horn-theory...